Monday 22 August 2005

P1
1400-1520 hours

073
The role of Indian Ocean Dipole in regional climate variabilities
Behera, Swadhin¹, Luo, Jing Jia¹, Masson, Sebastien¹, Yamagata, Toshio²
1 FRCGC/JAMSTEC, Yokohama, Japan
2 DEPS, The University of Tokyo, Japan
Author email: behera@jamstec.go.jp
The role of the Indian Ocean in climate variability has been well-recognized following the discovery of the Indian Ocean Dipole (IOD) mode. The coupled mode that peaks in boreal fall is marked as a dipole in the sea surface temperature (SST) anomaly and precipitation anomaly. Precipitation is suppressed (enhanced) in the eastern (western) Indian Ocean during a positive IOD event. This observed feature is well captured by a 200-yr SINTEX-F coupled model simulation. It is found that the IOD influence on East Africa short rains overwhelms that of the El Niño/Southern Oscillation (ENSO). On the eastern side, IOD influences the Darwin region thereby affecting the Southern Oscillation. The interaction between IOD and ENSO is an active topic of research (e.g. Yamagata et al. 2004). This is explored by decoupling the tropical Indian and Pacific Oceans in a couple of model experiments. Though IOD and ENSO could evolve independent of each other in model solutions, there are mutual interactions when both coevolved. The western pole of a positive IOD is warmer when accompanied by a warm ENSO. Conversely, El Niño terminates early in the presence of a positive IOD event. Analyses of observed data and idealized model experiments demonstrate the IOD teleconnection to Europe and midlatitude north Pacific. The IOD teleconnection is also traced to the La Plata region of the South America. The circumpolar wave trains along the Great Circle in boreal fall originate from the Rossby wave source generated by the atmospheric diveregence/convergence related to IOD.

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